The present invention relates to a liquid jetting head such as a recording head for an ink jet type recording apparatus, a coloring material jetting head for a display manufacturing apparatus, an electrode material jetting head for an electrode forming apparatus or an organism jetting head for a biochip manufacturing apparatus, and a nozzle plate provided in the liquid jetting head and a method of manufacturing the nozzle plate.
A liquid jetting head can jet a liquid in a droplet state and typically includes a recording head used in an image recording apparatus such as an ink jet type printer or an ink jet type plotter and serving to jet a liquid ink. In addition, examples of the liquid jetting head include a coloring material jetting head used in a display manufacturing apparatus for manufacturing a color filter such as a liquid crystal display and serving to jet a liquid coloring material such as R (Red), G (Green) or B (Blue), an electrode material jetting head used in an electrode forming apparatus for forming an electrode such as an organic EL (Electro Luminescence) display or an FED (face emitting display) and serving to jet a liquid electrode material, and an organism jetting head used in a biochip manufacturing apparatus for manufacturing a biochip (a biochemical element) and serving to jet a liquid bioorganism.
In the liquid jetting head of this kind, a pressure generation chamber and a nozzle orifice are communicated with each other and a droplet is jetted from the nozzle orifice by utilizing a fluctuation in a pressure which is generated over a liquid in the pressure generation chamber. In general, tens to thousands of nozzle orifices are provided in a line to constitute a nozzle array, and a plurality of nozzle arrays are provided transversely. The nozzle orifice is fabricated by punching (a kind of plastic working) using a die and a punch. As shown in FIG. 7, a punch 1 is a round punch, for example, and has a base portion 2, a taper portion 3 and a straight portion (a cylindrical portion) 4, and is used in a fixation state to a punch holder (pressure receiving plate) 5. For example, a plurality of punches 1 are arranged and attached in a line with the base portion 2 turned toward the punch holder 5 side and each of the punches 1 is brought down toward a material plate 6 (a work for forming a nozzle plate, see FIG. 8), thereby pushing the straight portion 4 and the taper portion 3 into the material plate 6. At this time, as shown in FIG. 8, the direction of the arrangement of the punch 1 is aligned with the direction of the nozzle array 7, thereby carrying out the punching. Accordingly, a plurality of provisional holes 7 (that is, concave portions to be the nozzle orifice) corresponding to one nozzle array are fabricated by one-time to several time working. It is also possible to set the attachment pitch of the punch 1 to be a double and to move the punch holder 5 in the direction of the nozzle array corresponding to a nozzle pitch after the fabrication is carried out by the previous working, thereby forming a provisional hole in the middle of the provisional holes fabricated previously.
When the punch 1 is pushed into the material plate 6, the straight portion 4 and the taper portion 3 enter in a vertical direction while applying plastic deformation to the material plate 6. By pushing in the punch 1, the material plate 6 flows in conformity with the straight portion 4 and the taper portion 3 in the punch 1 so that a provisional hole having a shape in conformity with the punch 1 is formed. Moreover, a part of the material plate 6 is pushed into the concave hole of the die so that a bulged portion is formed. When the punch 1 is sufficiently pushed in, the punch 1 is lifted to be separated from the material plate 6 and the bulged portion is removed by polishing. Consequently, a nozzle orifice penetrating through the material plate 6 in the vertical direction is fabricated. The nozzle orifice thus fabricated acts as a funnel-shaped through hole including a straight portion and a taper portion.
The nozzle orifice requires very high precision in a dimension and a shape. For example, it is necessary to set the taper angle of the taper portion, the inside diameter of the straight portion and the length of the straight portion within a tolerance having very high precision. The reason is that the jet characteristic or flight direction of a droplet is varied due to a variation in the dimension or shape of the nozzle orifice. In the related manufacturing method, however, it is hard to set the dimensions and shapes of the nozzle orifices to be equal to each other with high precision.
The foregoing will be described based on a punch and a punch holder which are illustrated in FIG. 9. A first punch 1a positioned on a left end in FIG. 9A can form the ideal profile of the nozzle orifice, and a straight portion thereof has a diameter φd0, the straight portion has a length L0 and an attachment dimension from the pinch holder 5 to a punch tip is h0. The “nozzle profile” implies the shape of the nozzle orifice formed on a nozzle plate (that is, formed in conformity to a punch) by sliding with the punch. In a second punch 1b positioned adjacently to the first punch 1a on the right side, a straight portion has a larger diameter φd2 than that of the first punch and other portions have dimensions L0 and h0 which are equal to those of the first punch. In a third punch 1c positioned adjacently to the second punch 1b on the right side, a straight portion has a diameter φd0 and a length L0 which are equal to those of the first punch 1a, and an attachment dimension from the punch holder 5 to a punch tip is h3 which is shorter than that of the first punch 1a. In a fourth punch 1d positioned adjacently to the third punch 1c on the right side, a straight portion has a diameter (φd0 and a length L0 which are equal to those of the first punch 1a, and an attachment dimension from the punch holder 5 to a punch tip is h4 which is longer than that of the first punch 1a. In a fifth punch 1e positioned adjacently to the fourth punch 1d on the right side, a diameter of a straight portion and an attachment dimension from the punch holder 5 to a punch tip are φd0 and h0 which are equal to those of the first punch 1a, and the straight portion is a length L5 which is smaller than that of the first punch 1a. 
In the case in which a plurality of provisional holes constituting one nozzle array are processed at the same time by the punches 1a to 1e, a material plate has a sectional shape shown in FIG. 9B after the punching and the material plate has a sectional shape shown in FIG. 9C after the bulged portion formed on the back side is removed. In a first nozzle orifice having an ideal profile by processing with the first punch 1a, it is assumed that a straight portion has a length m0 and a diameter φd0. In this case, in a second nozzle orifice processed by the second punch 1b, a straight portion has a length m0 in the same manner as the first nozzle orifice and the diameter φd1 of the straight portion is larger than the diameter φd1 of the first nozzle orifice. In a third nozzle orifice processed by the third punch 1c, moreover, a straight portion has a greater length m3 than the length m0 of the first nozzle orifice because the attachment dimension h3 of the third punch 1c is smaller than the attachment dimension h0 of the first punch 1a. To the contrary, in a fourth nozzle orifice processed by the fourth punch 1d, the entrance depth of a punch tip to the material plate 6 is greater than that of the first punch 1a because the attachment dimension h4 of the fourth punch 1d is greater than the attachment dimension h0 of the first punch 1a. As a result, the length m4 of the straight portion is smaller than the length m0 in the first nozzle orifice. In a fifth nozzle orifice processed by the fifth punch 1e which originally has a shorter straight portion than that of the first punch 1a, furthermore, it is a matter of course that the length m5 of the straight portion is also smaller than the length m0 in the first nozzle orifice.
Thus, the dimension of the nozzle orifice formed finally is varied and the jet characteristic of a droplet is varied for each nozzle orifice due to a variation in the dimension of the punch 1 or a variation in an attachment state to the punch holder 5. For example, when the length of the straight portion is too great, a jet efficiency is deteriorated so that the amount of a jetted liquid is decreased at a driving voltage according to a design value. As a result, the driving voltage is to be raised. To the contrary, if the length of the straight portion is small, a meniscus (a free surface of a liquid exposed from the nozzle orifice) is apt to be influenced by the surplus vibration of a liquid stored in a pressure generation chamber. Consequently, there is a drawback that a jet stability, that is, a stability of the amount of a droplet or a flight direction is deteriorated.
If the length of the straight portion in the nozzle orifice is managed to be 20 μm±5 μm, it can be guessed that a variation in a profile of each nozzle orifice can exceed an acceptable value in a related method of simultaneously processing the nozzle orifice in a line by using a plurality of punches 1 in consideration of the cause of a variation such as processing precision in the punch 1, precision in the attachment of the punch 1 to the punch holder 5, precision in the push-in dimension of a processing machine or precision in the processing of removing the bulged portion.